SPINAL MARROW. 329 



ter having converged regularly towards it.* The different 

 opinions of anatomists on the existence of this fissure may be 

 accounted for by its being readily found in early life, while it 

 is obliterated or very indistinct in old age. This lateral fissure 

 should be carefully distinguished from two others, one before 

 and the other behind it, which extend the whole length of the 

 medulla spinalis, and consist in a series of little depressions, 

 running into each other and transmitting the filaments which 

 form the roots of the spinal nerves. The posterior, of the last 

 named lateral fissures, is deeper than the anterior, and pene- 

 trates in the same direction with the lateral fissure first men- 

 tioned; it also, in. like manner, joins its fellow, but only after 

 having proceeded to within a few lines of the inferior end of the 

 medulla spinalis. 



The substance of the spinal marrow being of two kinds, ci- 

 neritious and medullary, the order of their position is reversed 

 from what occurs in the brain; for the cineritious is included or 

 enveloped by the other. On making a transverse section, the 

 cineritious will be found much less abundant than the other, 

 and consisting of a thin transverse lamina in or near the centre 

 of the medulla: this part is joined at either end to a portion 

 somewhat crescentic, whose concavity is outwards, and the con- 

 vexity inwards. The transverse part does not run into the 

 middle of the crescent, but somewhat anterior to the middle, so 

 that the anterior horn is shorter than the other, and is also 

 thicker and obviously more obtuse. The cineritious or grayish 

 substance is more abundant at the lower part of the medulla 

 spinalis than it is above. In the foetus, at the end of gestation, 

 it predominates below, occasionally, to the entire exclusion of 

 the other. The medullary or white substance is more abundant 

 laterally than elsewhere, and has its two symmetrical sides joined 

 together by a thin lamina at the bottom of the anterior and of 

 the posterior fissure. 



Each half or symmetrical side of the medulla spinalis is itself 

 divided into two chords, marked off from each other by the pos- 

 terior horn of the cineritious crescent, and by the first described 

 lateral fissure. Of these chords the anterior is, consequently, 

 much the larger; it is also longer and forms the inferior extre- 



* Mcckel, Minuel D' Anatomic, 

 29* 



